PROJECT SUMMARY/ABSTRACT Incidence of obesity continues to escalate in recent years with increasing consumption of high fat meals, leading to significant increase in risk and incidence of metabolic diseases including diabetes and cardiovascular disease. The current strategy for obesity/diabetes management is not optimal with bariatric surgery being the most effective. However, the potential risk of surgical procedures has limited its use to clinically severe obese individuals. Therefore, the development of novel therapeutics that can mimic the metabolic benefits of bariatric surgery is highly desirable. Our earlier studies revealed that inactivation of the group 1b phospholipase A2 (PLA2g1b) gene in mice resulted in metabolic benefits similar to that observed with bariatric surgery, including resistance to high fat diet (HFD)-induced obesity, improved glucose tolerance to alleviate hyperglycemia, and resistance to HFD-induced dyslipidemia. Additional studies revealed that the gut microbiota of Pla2g1b-/- mice also resembled those present in mice with vertical sleeve gastrectomy (VSG) surgery, with both procedures suppressing HFD-induced increase of Firmicutes/Bacteroidetes ratio in the gut microbiota. Interestingly, we also observed significant reduction of PLA2g1b lipolytic products, lysophospholipids (LPC) and lysophosphatidic acid (LPA)/choline, in plasma and along the intestinal tract of mice after VSG surgery. These results indicated that PLA2g1b inactivation and VSG surgery phenocopy each other , with both procedures reducing LPC/LPA/choline levels and altering the gut microbiota to confer metabolic benefits. These data provided strong support for the premise that PLA2g1b inhibition may be a novel therapeutic strategy to recapitulate the metabolic benefits of bariatric surgery. The overall goals of this project are: (i) to identify the mechanism underlying the inter- relationship between PLA2g1b inactivation and bariatric surgery in modulation of the gut microbiota and metabolic disease risk, and (ii) test the hypothesis that pharmacologic PLA2g1b inhibition is a viable strategy for metabolic disease intervention. Aim 1 will test the hypothesis that lipid nutrient metabolites generated by PLA2g1b hydrolysis of luminal phospholipids are responsible for the altered gut microbiota in response to HFD. This aim will identify the specific influence of LPC, LPA, and/or choline in dictating the gut microbiota and metabolic disease risk. Aim 2 will identify the mechanism underlying the sustained metabolic benefits of VSG surgery. This aim will test the hypothesis that VSG surgery elevates intestinal expression of the LPC re- esterification enzyme LPCAT3 to reduce intestinal LPC/LPA/choline levels with the accompanying metabolic benefits. Aim 3 will test the hypothesis that PLA2g1b inhibition reprograms the gut microbiota to reverse and improve obesity and diabetes. A segregating panel of 8 genetically diverse inbred mouse strains will be used to evaluate the effectiveness of PLA2g1b inhibition for obesity/diabetes intervention in a genetically diverse population. Completion of this study will fill a knowledge gap regarding how dietary nutrients modulate the gut microbiota and how modulating nutrient processing in the digestive tract may confer metabolic benefits.